In some embodiments, the present disclosure relates to new phosphoramidite compositions, that have Silyl-containing carbonate or thiocarbonate or ether as 5′-hydroxyl protecting groups useful fo the syntheis of RNA, and in particular for the synthesis of long sequences of RNA (e.g., >50 mer). In some embodiments, there are provided methods for simultaneous oxidation of the internucleoside phosphate triester linkages and removal of the 5′-hydroxyl-protecting group, making this process a new 2-step RNA synthesis, that involves the use of peroxyanions in combination with fluoride anions.